The United Kingdom and the European Union say they have agreed to a Brexit withdrawal deal. NPR's Frank Langfitt is on the line from London. Hey, Frank.

FRANK LANGFITT, BYLINE: Hey. Good morning, Noel.

KING: So it has been a journey.

LANGFITT: It has.

KING: What's...

(LAUGHTER)

KING: What's in this deal? What's in this deal, and how does it address the really big hurdle, which was, all along, the Irish border?

LANGFITT: Well, it looks at the moment as though the EU and the U.K. have managed to square this circle. And what they're going to do - the way the deal works is it actually will avoid the creation of customs posts along the border between...

KING: Oh.

LANGFITT: ...Northern Ireland and the Irish Republic. And that's really crucial because that would've been a disaster, frankly.

KING: Yeah.

LANGFITT: If they'd had to have customs posts, there was a fear of a return of violence from the days of the Trouble - Troubles. And the way they're going to do this is very creative and really is sort of the art of the possible in politics. The U.K., if you stay with me on this, is going to technically stay in the - Northern Ireland will stay, technically, in the U.K. customs territory. But let's say products go from Great Britain, which is, of course, England, Wales and Scotland, across the water into Northern Ireland and they might then end up in Ireland, which will be a part - of course, is still part of the EU. Then the United Kingdom would actually collect tariffs on behalf of the EU.

KING: OK.

LANGFITT: It's a way of, you know, kind of fudging this to some degree, but to avoid something much worse. The other big part of the element of this is that Northern Ireland - the elected representatives in Northern Ireland - because this is such an unorthodox deal and they want to make sure that the people of Northern Ireland agree to this, a number of years in the future, they would be able to vote on whether they want to keep this very unusual arrangement.

KING: Oh, so they will get to pick...

LANGFITT: Yes.

KING: ...At a certain point. Oh, that's really interesting.

LANGFITT: At a certain point, they - and so the thing - the concern was - I think, it's a legitimate concern - is to say, listen; you're going to stay in this really weird relationship where, of course, you're a part of the United Kingdom, but you're still more - you're closely aligned with the European Union in some ways. And how do the people of Northern Ireland feel about that? They will have a chance, through their elected officials, to decide on whether they want to keep this thing going.

KING: So is Brexit a done deal now? Can we say that?

LANGFITT: No.

KING: (Laughter).

LANGFITT: Brexit is never a done deal. This is going to go on for years. But the real problem now is domestic British politics for Boris Johnson, the prime minister. The Democratic Unionist Party of Northern Ireland does not like this deal. It is afraid that it may not be able to impose its will 'cause it's - if it wants to pull out of this deal, it may not have the political firepower, so to speak, to get out of this deal in the years ahead.

And so it is actually, right now, withholding its 10 votes in Parliament on this deal. And the vote is expected in Saturday if the EU, as we expect in the next couple of days, ratifies this. And Boris Johnson doesn't have a majority in Parliament, so he could find himself being very successful in Brussels and coming back home and actually being defeated on Saturday by his own party.

KING: Oh, that is really, really interesting. It isn't over.

LANGFITT: (Laughter) No.

KING: So let me ask you something. If we were to identify a winner in these long negotiations, who would it be?

LANGFITT: I think the EU.

KING: Yeah.

LANGFITT: I think all along, from Day 1, they had the leverage and the power, and Boris Johnson has actually had to make a lot of concessions here and even accept things that his predecessor Theresa May said she would never accept. But Boris Johnson has an election coming up. And he wants to deliver. He promised to do so. And that's what he says he's doing.